IES or ISRO: which is better for the ECE branch?

The winning institute cannot be unequivocally spotted here as the choice depends upon whether you want to land into a techno-managerial job or purely a technological job.

Here are the few listed points to study both the options:

Job Security: Both IES and ISRO are government jobs, hence the job security is implicit.

Job Reputation:

• ISRO is a reputed-job in India but IES is one of the most prestigious jobs in India. 
• IES gets a chance to network with the bureaucrats of India. 
• They are called "civil servants" of India. As they get promoted, there is a chance to be in a position that is on par with IAS.

Other Perks:

• IES gets a chance to travel within the various parts of the country for video conferences, while ISRO provides the opportunity to travel abroad for work.
• IES is a mix of management and technical jobs. You have to lead your subordinates along with working technically. IES can go for higher studies in management. 
• In ISRO you will have a purely technical job. You can opt for it if you are interested in growth opportunities in the technical field of work. If you want to pursue higher studies in a technical field then you can also go for this job.
• In ISRO you will get to work with many talented people from India and abroad.
• You get a promotion based on time in IES, not based on performance like in ISRO.
• IES gets a chance to get transferred and work with different departments or ministries. While in ISRO, you will be constrained to a single department.

These are the perks of both jobs. To decide which is better for you, choose what is the line of work you want to join.